23.3.1 Major release (November 01, 2009)

We would like to thank all of our users who have reported problems and made suggestions for improving this release. In particular, we thank Wolfgang Britz, Wietse Dol, Daniel T. Fokum, Nuri Gokhan, Iiro Harjunkoski, Josef Kallrath, Lloyd R. Kelly, Kristina Konold, and Uwe Schneider.

Assigning members to a set using the asterisk is now possible in decreasing order as well. For example, the following are valid set statements in GAMS.

Set years /bc2000*bc1,0*2009/;
Set years /"-20"*"-1"/;

The GAMS parameters ProcDir and MaxProcDir can be used to control the generation of process directories. ProcDir=abc will use abc instead of the 225. The user is responsible to create and remove the directories. %gams.procdir% will now be defined and give you the actual process directory in use. MaxProcDir=100 will extend the usual 225a to 225z, 225aa, 225ab, etc. The defaults will be 26 for MaxProcDir and 225? for ProcDir to make everything work as before.

The GAMS parameter RunDir was removed.

The Dollar Control Options $hiddencall does the same as $call but makes sure that the statement is neither shown on the log nor the listing file. This is also true in case $ondollar or dp=2 is used. $hiddencall is especially useful in case of an encrypted model that e.g. reads/writes from an password-protected Excel file using gdxxrw password option.

These new bare bone solver links come free of charge with the GAMS Base system. General GAMS options (reslim, optcr, nodlim, iterlim) are supported. In addition an option file in the format required by the solver can be provided.

CoinOS 2.0

The new experimental link to the Optimization Services project allows you to convert instances of GAMS models into the OS instance language (OSiL) format and to let an Optimization Services Server solve your instances remotely.

Simplex performance: The simplex optimizers are much faster in the release. The improvements are most pronounced in the dual simplex method.

MIP performance: The MIP solver is significantly faster as well. Part of this is a consequence of the increased speed of the dual simplex optimizer, and part is due to algorithmic improvements in the MIP itself.

MIP IIS: You can now compute an Irreducible Inconsistent Subsystem (IIS) for an infeasible MIP model. The previous release could only compute IISs for continuous models.

MIP node files: You can now store search tree nodes on disk. This allows you to solve much larger and more difficult MIP models. Use the new NodefileStart parameter to indicate how much memory you would like to devote to nodes before they are written to disk. The performance impact of putting nodes out to disk is typically quite small.